With iOS 10 Apple is changing the way that the "Limit Ad Tracking" setting works in Settings > Privacy > Advertising, and it seems to be causing a mini storm in a teacup among the adtech world.
According to "privacy thought-leader" Alan Chapell: "The net effect is Apple is enabling iOS10 users to effectively opt out of advertising."
Is this the case? Short answer, No. Long answer, lets jump back to 2011...
Every iOS device has whats called a UDID (Unique Device Identifier), which is a static string of characters, unique to your device, and cannot be changed. With the UDID, your device could be recognised between different applications, allowing advertisers & analytic services that developers use to build a profile of you to serve you more personalised adverts based on your behaviour and the apps you use.
In iOS 5, access to the UDID was deprecated. This means while it was still available, Apple was giving advanced warning that this would eventually be revoked.
When iOS 6 got announced, it came with a new API specifically for advertisers to use and give more control to the end-users. This was called IDFA (Identifier for Advertisers). This worked in a similar way to UDID, only instead of having a static ID per device, users could opt to reset the IDFA at any time or "Limit Ad Tracking" where a developer has to agree that their app honours this setting while submitting an app.
Changes in iOS 10
So in iOS 10, the functionality of "Limit Ad Tracking" is changing. Previously, turning it on would randomise your IDFA to a new string and set a flag that you have requested to limit tracking. As this new string was static until you have requested to reset it or disable "Limit Ad Tracking", it could still be used to track you, but Apple believed that developers & advertisers would follow its rules and ignore it for behavioural purposes. I doubt many app developers checked the code of their advertisers of choice to see if they conformed to "Limit Ad Tracking" when including their SDK, and I have no doubts that many abused this or simply not understood it.
In iOS 10, when you enable "Limit Ad Tracking", it now returns a string of zeroes. So for the estimated 15-20% of people who enable this feature, they will all have the same IDFA instead of unique ones. This makes the IDFA pretty much useless when "Limit Ad Tracking" is on, which is a bonus, as this is what users will expect when they enable the feature. These users will still be served ads, but its more likely they will not be targeted to them based on their behaviour.
If you want to test the IDFA functionality, I made an example project for iOS which you can test in the iOS 9 & 10 simulators to test the differences, and the Apple API documents for this are hosted here.
I personally think this is a great change for iOS, although personally I would prefer this option to be presented to the user during on boarding, enabled by default, or no longer hidden under several menu layers. My main concern however from the editorial was this quote in particular:
For advertisers, they should notice minimal differences assuming that they are honouring the "Limit Ad Tracking" preference. This quote seems to suggest that some(most?) advertisers are not honouring this option and their business models rely on 100% behavioural tracking. Losing the 15-20% of people who opt-out breaks their advertising model forcing them they try more "intrusive" methods to profile you. This further proves that the advertising industry cannot be trusted to self-regulate itself when it comes to honouring user privacy and is one of the many catalysts that turn people to adblock tools, such as Crystal, for their privacy needs.
I'll end with this quote from this article on Digital Content Next by Chris Pedigo: